Classification of materials used in circuit connections and components :
In a typical electrical circuit, charge is confined to flow in conductors and various circuit components that are connected to these conductors. The analogy to this mechanically, could be a water pump for the voltage source, water for the charge and pipes as the conductors, where water is confined to flow only through the pipes.
The following electrical circuit shows a battery as the voltage source which is being used to deliver energy to the circuit. There is also a lamp in the circuit, giving off light and some heat which is using the energy that is being supplied by the source. The connection mechanism that allows this energy transfer from the source to the lamp is two wires (conductors). There is one wire connected from the source to the lamp and another from the lamp back to the source, completing the circuit.
Fig.- 7
The wires in this circuit are the conduit that allows the charges to carry the energy from the battery to lamp. The lamp essentially uses up most of this energy leaving only a very small amount to allow the charges to return to the source. Once the charges enter the opposite end of the source they gain energy from the chemical process in the battery and are ready to supply energy to the circuit all over again, completing the cycle.
In this process it is desired to make the delivery system from source (battery) to Load (lamp) as lossless as possible. This is accomplished by using conductors (wires) as the delivery system. The conductor of choice in most electrical systems is copper since its cost, availability and energy loss characteristics are reasonable.
Most metals will make decent conductors, some better than others. The best conductor is Gold, then followed by Silver, Copper and Aluminum when considering energy loss characteristics.
V1 100 V X1 100V_100W
+
-+
-Conventional Current Flow
I
I
Battery
Lamp
+
+
Energized Charge De-energized Charge 1 0 wire wireLooking at the Copper atom below, which has 29 Protons and Neutrons in its nucleus and 29 electrons
Fig.- 8
in various shells orbiting around it when in isolation. The important thing to note here is that there is only one electron in its valence shell, which at room temperature gains enough energy to be free of the atom to roam around the Copper material. It’s this free electron that gives Copper it’s good conductivity (low energy loss characteristics).
This is a good point in this discussion to look at the three general classifications of materials that are encountered in electrical circuits.
General Electrical Material Classifications:
Conductors:
A conductor is a material through which electric charges move easily at room temperature. The material most commonly used are metals. Good conductors have large numbers of free electrons that are readily available for conduction. This implies the outer valance shell has 3 or less electrons which depending on the metal can be free for conduction at room temperature. Some example are Copper, Gold, Silver and Aluminum, these are all considered excellent conductors. The most widely used conducting material is Copper because it is relatively inexpensive, an excellent conductor and easily formed into wire. Wires that are used to interconnect various circuit components are generally made of copper, The wires are shown as lines in circuit diagrams (schematics) that electrically connect all the circuit components together.
Gold and Silver are better conductors but are very expensive. Gold oxidizes much less than the other metals and is therefore used as plating on electrical contacts to minimize contact resistance on good quality, high reliability components. Aluminum is not as good a conductor as Copper but is much lighter and is used where conductor weight is a factor like in overhead power transmission lines.
Insulators are materials that do not conduct electrical charges at room temperature because they have nearly full or full valence shells hence all their electrons are tightly bound to the lattice atoms. Examples of insulators are glass, plastic, rubber, Bakelite, etc. Insulators are generally used with conductors as a covering to protect other conductors making contact with each other or form us making contact with the conductor and getting an electrical shock. However it should be noted that insulators can become conductors if subjected to very high voltages. This causes break down in the material ripping electrons from the outer shell which then become available for conduction.
Another example of how insulation material can be used to isolate a circuit would be a switch. The switch is a mechanical device that mechanically either connects or disconnects a power source to a circuit. So effectively, the switch is used to mechanically make or break a wire connection in a circuit. Without the use of a switch like in the previous circuit, the lamp could never be shut off. If one of the wires was disconnected, the lamp would shut off but this would not be convenient if all the wires were soldered to each component. However, if a switch was added to the circuit the circuit wiring could remain complete because it could be used to open or close the connection to the circuit components. Note in a switch the insulator is generally air since the switch internally just breaks the wire connection when flipped in the off position by opening as set of contacts designed for that purpose.
Semiconductors:
Semiconductors such as Silicon, Germanium and a few other materials have half filled valence shells making them neither good nor poor conductors. One of the most widely used semiconductor materials used today is Silicon. By doping the base semiconductor material with very specific elements one can make the materials conduction properties change voltage, heat light, etc. Examples of some
semiconductors are diodes, transistors, integrated circuits etc.
In general these are what is called active devices, meaning they might give a circuit a current or voltage gain or both. Two examples are transistors and operation amplifiers.
Technically any material that offers some appreciable resistance to the flow of charge can be a semiconductor because it would be somewhere between a conductor(virtually no resistance to the flow) and an insulator (allowing practically no flow of charge). So a passive device like a simple resistor which is used to limit current flow, can be considered a semiconductor. Resistors allow varying amounts of charge to flow depending on their resistance value. They are considered passive devices because they only dissipate energy as heat.
Typical sources commonly used in electrical circuits :
In electrical engineering there are two basic types of sources 1. DC voltages and current sources.
Most of the discussion here will focused on DC voltage sources since our initial discussion of circuits and circuit theory is best understood using DC analysis. AC source will be briefly discussed were necessary and current source just once as a Norton source since its application is used mostly in advanced courses.
DC Sources (Batteries):
Types of batteries :
1. Alkaline, terminal voltage = 1.5 volts. 2. Carbon Zinc, terminal voltage = 1.5 volts. 3. Nickel Cadmium, terminal voltage = 1.5 volts.
4. Lithium, terminal voltage can from 2 volts to 3.5 volts, button cell type. 5. Mercury, terminal voltage = 1.4 volts, no longer available.
6. Lead acid, terminal voltage from 6 volts, 12 volts, etc, 2 volts/cell, typical automotive uses.
Typical Batteries used in everyday applications :
Fig.- 10
The above photograph shows two “AA” type (AA Cell) batteries connected in series and two “AA”type (AA Cell) connected in Parallel. The photo also shows two larger capacity “C”type (C Cell) and “D”type (D Cell) and a 9 volt batteries.
The table below is small sample of some typical milli-Amp-Hour (mAH) ratings of various sizes of batteries in everyday use. The first five types are 1.5 volt Alkaline and the last is a Lead-Acid ( typical 12
Battery Type
Capacity (mAh) Typical Drain (mA)
D
12000
200
C
6000
100
AA
2000
50
AAA
1000
10
9 Volt
500
15
12 Volt Car Batt.
50000 - 70000
1000
Fig.- 11
The battery life for example for “AA” battery would be,
T (battery life, hours) =
𝐂𝐚𝐩𝐚𝐜𝐢𝐭𝐲 (𝐦𝐀𝐇) 𝐂𝐮𝐫𝐫𝐞𝐧𝐭 𝐃𝐫𝐚𝐢𝐧 (𝐦𝐀𝐇)=
𝟐𝟎𝟎𝟎
𝟓𝟎
= 40 hours at 50 ma ( 8 )
The schematic representations of two batteries in series and two in parallel are shown in the following diagram. It is very important to note how the polarity of the batteries is connected in each case. The symbol of the battery is a long line over a short line where the long line represents the positive terminal and the short line the negative terminal in the diagram. This symbol is called a Cell.
Fig.- 12
It should be noted that the AA, AAA, AAAA, C and D batteries are considered basic cells whose terminal is 1.5 volts. There are many other types of battery packages sold with higher terminal voltages and/or higher current ratings using these basic cells connected internally in various configurations.
The terminal voltage of a batteries basic cell is a function of its chemical makeup. The batteries just discussed basic cell is 1.5 volts. Battery packs using these cells can have terminal voltages of 3.0 v, 4.5 v, 6.0 v, etc., multiples of 1.5 v. However the lead-acid car batteries basic cell is 2.0 volts which implies a
V1 1.5 V V2 1.5 V V3 1.5 V V4 1.5 V 1 4 5 2 3 + + + + + + _ _ _ _ _ _ Two Batteries Connected in Series Two Batteries Connected in Parallel
Electrical Schematic showing the connection of two 1.5 volt Cell Batteries
3.0 volts 1.5 volts
Twice the voltage, same current.
Same voltage, twice the current.
12.0 volt battery is made up of six 2.0 v cells connected in series. A motorcycle battery would have three basic cells connected in series to give a terminal voltage of 6.0 volts. So keep in mind that batteries cannot have just any voltage because the terminal voltage must be some multiple of its basic cell voltage which is a function of the cells chemical makeup.
Batteries are obviously the way to go for portable applications but are not the best option for non-portable bench applications or situations where you need a voltage that is not some multiple of a basic cell voltage. In these situations we use what is known as a bench Power Supply or more commonly known as a Power Supply.
Power Supply :
These power supplies all plug into various configurations of building AC 120 volt and 240 volt, 60 Hz distribution systems here in the United States. The energy supply for these power supplies is for example, the 120 v AC wall outlet, not a chemical reaction as in the battery. The basic design of these supplies is to take the AC input and convert it to DC and then use the DC to power an electronic circuit which is designed to deliver fixed or variable DC voltages at user available output terminals. There are two basic types of these supplies,
1. Laboratory fixed and variable output DC supplies which can be used to replace the portable battery when portability is not needed. Also one of the neat features of these supplies is that the output voltage can be set to any voltage value that is within the supplies designed output range.
2. AC to DC adapters sometimes called Wall Warts. These in general are fixed output voltage units specifically designed to replace batteries in a portable piece of equipment when portability is not needed at that time or to recharge special rechargeable battery packs in that equipment. One must be careful when using these Wall Warts since they come in various voltages and power ratings. Using a Wall Wart with a power rating that is less than what is needed will cause the Wall Wart to burn out and possibly catch fire.
Fig.- 14
Other types of sources :
Below is a brief list of some other types of sources. They are being listed here for identification purposes only and any further explanation will be presented as the need arises.
Solar Cells :
Converts light energy into electrical energy. Available in a large variety of voltage and current ratings.Thermopile : Converts thermal energy into electrical energy. The thermocouple would be an
example of this.
Current Sources :
These are essentially active electronic sources which can deliver a specified current to varying circuit loads. These are used a lot in circuit modeling in moresophisticated electronic devices. For example, A DC current source will deliver a constant current to any branch of a circuit that it is located in. In other words a current source defines the value of current in the conductor in which it is located.
